When do symptoms of AIDS typically appear during HIV infection?

When a significant number of helper T-lymphocytes are damaged by HIV

The correct answer is Option (3) - When a significant number of helper T-lymphocytes are damaged by HIV

The symptoms of AIDS usually appear when HIV (Human Immunodeficiency Virus) has caused significant damage to the immune system, particularly the helper T-lymphocytes. Here is a detailed explanation of each option:

(a) Within 15 days of sexual contact with an infected person: This option refers to the acute stage of HIV infection, also known as the primary infection stage. During this stage, individuals may experience flu-like symptoms such as fever, fatigue, sore throat, swollen lymph nodes, and rash. However, these symptoms are not specific to AIDS and can occur in other viral infections as well. It is important to note that the presence of these symptoms does not necessarily indicate the development of AIDS.

(b) Upon entry of the infected retrovirus into host cells: This option describes the early stages of HIV infection, where the virus enters the host cells, particularly the CD4+ T-lymphocytes. HIV replicates inside these cells and gradually depletes their numbers over time. However, during this stage, individuals may not show any noticeable symptoms of AIDS.

(c) When a significant number of helper T-lymphocytes are damaged by HIV: This option is the correct answer. HIV primarily targets and infects helper T-lymphocytes, which are crucial for coordinating the immune response. As HIV replicates and damages these cells, the immune system becomes progressively weakened. Once a substantial number of helper T-lymphocytes are depleted, individuals are more susceptible to opportunistic infections and the symptoms of AIDS start to appear.

(d) When reverse transcriptase produces viral DNA: Reverse transcriptase is an enzyme used by HIV to convert its RNA genome into DNA, which can then integrate into the host cell's DNA. This step is crucial for HIV replication, but it does not directly correlate with the appearance of symptoms or the development of AIDS.

In summary, the symptoms of AIDS typically become evident when a significant number of helper T-lymphocytes are damaged by HIV, leading to a weakened immune system. It is at this stage that individuals are more susceptible to opportunistic infections, cancers, and other complications associated with AIDS.